Fig. 1. (A) Organization of the Ori1 replication origin in A.
pernix. The four ORB sequences are located on either side of the
DUE. The sequence of the 5'-to-3' ("top") strand of ORB4 is
shown. (B) Overall structure of the ORC1-DNA complex. (C)
Contacts between the AAA^+ domain and DNA. Thr^122 (T122) (21)
contacts the Gd18-Cd5 base pair, L124 main chain oxygen contacts
Gd19, and E128 contacts Gd20 via a water molecule. Residues
T103, R106, G123, and R132 make direct interactions with the
phosphodiester backbone on either side of the minor groove. (D)
Insertion of the wing of the WH domain into the DNA minor groove
widens it by 5 Å. Residues S366, G368, G371, and K372
interact directly with bases Td17, Gd18, and Gd19 of the
complementary strand. G368, G371, K372, and T373 also interact
with the DNA backbone on both sides of the minor groove. (E)
Insertion of the recognition helix of the WH domain into the
major groove. R345 makes a base-specific interaction with Gd10.
Residues T343, R346, S348, and R374 contact the DNA phosphate
backbone. The R346 side chain is stabilized in a noncanonical
conformation by a salt bridge interaction with E353, which
enables it to bind the DNA phosphate backbone. In the same way,
interaction between S352 and R374 brings the arginine side chain
close to the DNA backbone.